The present invention relates generally to distributed computing systems, and more particularly to a method and apparatus for dynamically expanding a RAID (Redundant Array of Independent Discs) set while assuring data integrity during the expansion process.
In a distributed computing system, a host is connected to a storage (memory) system via a storage controller. The host communicates with the storage controller through an interface, such as a small computer systems interface (SCSI). RAID technology is often employed to provide data redundancy for distributed computing systems. In a RAID architecture system, the host communicates to a RAID storage controller via an interface (SCSI). In turn, the RAID storage controller is connected to one or more storage elements (i.e., the RAID set, which may include hard disc drives, optical discs, or magnetic tape drives) for storing host data. The host writes to or reads from the storage elements through the RAID storage controller. The RAID storage controller writes data to the various storage elements according to the user's selected RAID level providing the user a selectable level of redundancy for host data.
In some systems the number of storage elements for storing the host data is variable. That is, the number of storage elements is dependent on the amount of information required to be stored. Accordingly, for some systems, expansion to add one or more storage elements to the existing RAID set is required as host storage requirements increase.
One problem that has arisen during RAID set expansion is maintaining data integrity for the system in the event of a failure during the expansion process. While ordinarily data integrity is high because of the redundancy built into the RAID architecture system, during the expansion process, singular failures may result in data loss. In order to assure data integrity, some systems disable storage operations during the expansion process, thereby disabled the host from accessing the system storage. While this allows for easier configuration control over the storage system, it results in inefficiencies in the host. What is desired is to provide for dynamic expansion capability while maintaining host data integrity.